Short tandem repeat (STR) DNA sequences are interspersed throughout the human genome. These loci are highly polymorphic with respect to the number of repeat units they contain and may vary in internal structure as well. Variation in the number of STR repeat units at a particular locus causes the length of the DNA at that locus to vary from allele to allele.
While the alleles at a single STR locus may be the same for two different individuals in a population, especially if the individuals are genetically related, the probability that the alleles of any two unrelated individuals will be identical at several different STR loci becomes smaller and smaller as the number of loci examined increases. By determining the alleles at a sufficiently large number of STR loci it becomes possible to establish with virtual certainty whether or not two biological samples came from the same individual.
In forensic casework, it is common to encounter evidence samples, like vaginal swabs from a rape victim, which contain a high concentration of DNA from one source, the victim of rape, and only a small concentration of DNA from the perpetrator(s). In such instances the analyses of autosomal DNA will likely result in the perpetrator's autosomal STR profile being masked by the presence of the victim's DNA present in the mixture. This is problematic since the most prevalent DNA criminal databases rely largely on autosomal STR loci for individual identification.
The instant disclosure offers solutions to the challenge of determining the autosomal STR profile of a perpetrator in the presence of excess victim's DNA as well as other challenges.